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Linux network bridge devices.

When you’re setting up a virtual machine on Linux using KVM/QEMU, you’ll more than likely need to setup a bridged network device.

I’ve done this now a couple of times, and both times the network has “hung” during bootup. It seems that this is because I’m also enabling an MTU size of 9000 (Gigabit ethernet with jumbo frames) using the mtu stanza in the br0 section of /etc/network/interfaces.

This is Not The Done Thing, by all accounts. When setting up the MTU on a bridge device, one apparently needs to use the post-up stanza to add the command

ifconfig eth0 9000

to the interface. This sets the mtu on the interface which br0 is bridging – in my case eth0, you’ll need to edit to suit your configuration.

This will solve the long bootup problem, and cause jumbo frames to be enabled at the point the interface is brought up. When connecting to my iSCSI target on the SAN, this makes the transfers no end quicker.